1. Field of the Invention
The present invention relates to a method for treating a waste liquid from a wet exhaust gas treating device.
2. Description of the Prior Art
Heretofore, a waste liquid from a wet exhaust gas treating device must be additionally treated, since it cannot be discharged directly to a drain or the like. For example, a waste liquid diminishing system is utilized in which the waste liquid is introduced into a flue connecting to a dust collector and is treated therein, and now, this system will be described in reference to FIG. 2.
An exhaust gas from a boiler 11 is guided through a flue 12 to an air heater 13 in which the exhaust gas is heat exchanged with air, whereby a temperature of the exhaust gas falls. The exhaust gas coming from the air heater 13 is led to a dry electric dust collector 2 through a flue 8. In the middle of the way, a waste liquid is sprayed into the flue 8 through a spray nozzle 1, so that the temperature of the exhaust gas drops.
In the dry electric dust collector 2, a dust in the exhaust gas and the waste liquid are dried to produce a solid material, and the latter is collected therein. The collected solid material is transported to an ash collector (not shown) by means of an ash transport device 6.
The exhaust gas which has left the dry electric dust collector 2 is led through a flue 14 to a gas heater 15, in which the exhaust gas is heat exchanged with a gas coming from a wet exhaust gas treating device 17, so that the temperature of the exhaust gas falls.
The exhaust gas from the gas heater 15 is guided to the wet exhaust gas treating apparatus 17 through a flue 16. In the wet exhaust gas treating device 17, a sulfurous acid gas in the exhaust gas and a dust which has not been collected by the dry electric collector 2 are further collected and removed therefrom.
The exhaust gas coming from the wet exhaust gas treating device 17 is introduced through a flue 18 into the gas heater 15 in which heat exchange is carried out, and it is further delivered via a flue 19 to a chimney 20, and is then discharged therethrough into the atmosphere.
The waste liquid from the wet exhaust gas treating device 17 is guided to a neutralizing tank 22 via a waste liquid line 21. In the neutralizing tank 22, slaked lime is introduced through a neutralizer line 23 in order to neutralize the waste liquid. The thus neutralized waste liquid is guided to the waste liquid spray nozzle 1 through a waste liquid line 24, and is then sprayed into the flue 8.
Now, reference will be made in accordance with FIG. 3 to the feature of a conventional constitution between the waste liquid spray nozzle 1 and the dry electric dust collector 2 in the waste liquid diminishing system.
The dry electric collector 2 has a conventional structure. At an upstream position of the collector 2, the spray nozzle 1 is disposed. The waste liquid sprayed through the spray nozzle 1 is evaporated and thereby dried in the flue 8, but a part of the dried substance is accumulated as an in-flue deposit 7 in the flue 8. The major remaining dried solid material 5 is collected by a discharge electrode 3 and a dust collecting plate 4 in the dry electric dust collector 2, and is then transported to the ash collector by means of the ash transport device 6 disposed under the dust collector 2.
In this connection, the liquid droplets sprayed through the spray nozzle have to reside in the exhaust gas for a period of about 2 seconds for the sake of its evaporation. On the other hand, a gas flow rate in the flue is usually within the range of 15 to 20 m/sec, and thus the flue having as extraordinarily great a length as that of about 30 to about 40 meters is necessary. If the above mentioned gas flow rate is lowered, the dust will be accumulated in the flue.